Low boron amorphous alloy having excellent soft magnetic characteristics

ABSTRACT

A low boron amorphous alloy having excellent soft magnetic characteristics, composed of B: about 6-10 at %, Si: about 10-17 at %, P: about 0.02-2 at % and the balance Fe and incidental impurities. The invention lowers production costs because the content of expensive boron is reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a low boron amorphous alloy having excellent soft magnetic characteristics, and more specifically to a low boron amorphous alloy in which the boron content is advantageously reduced without deteriorating the magnetic characteristics of the alloy.

2. Description of the Related Art

Various Fe-Si-B alloy compositions are known to possess excellent soft magnetic characteristics.

For example, U.S. Pat. No. 3,856,513 discloses an amorphous alloy containing at least 80 at % Fe, at least 10 at % B and no more than 6 at % Si. Further, U.S. Pat. No. 235,064 discloses an amorphous alloy composed of 77-80 at % Fe, 12-16 at % B and 5-10 at % Si.

Almost all known Fe-Si-B amorphous alloys contain at least 10 at % B, as B is very important to the amorphous property of such alloys. The higher the B content, the stronger the amorphous forming capability of the alloys, whereby thermal stability is improved. Thus, it has been conventionally believed that a B content of at least 10 at % is required to produce excellent soft magnetic characteristics in Fe-Si-B amorphous alloys.

Further, both iron loss and magnetic flux density of conventional Fe-Si-B amorphous alloys containing less than 10 at % B are inferior to alloys containing at least 10 at % B.

Because of the high cost of B, there have been attempts to improve Fe-Si-B amorphous alloys containing less than 10 at % B. For example, C has been added to stabilize age deterioration and to improve amorphous property forming capabilities (Japanese Patent Unexamined Publication No. 57-145964 (1982) and Japanese Patent Unexamined Publication No. 58-42751 (1983)), Mn has been added to improve surface treatment properties (Japanese Patent Unexamined Publication No. 61-136660 (1986), and Cr has been added to improve casting properties (Japanese Patent Unexamined Publication No. 58-210154 (1983)). However, maintaining excellent soft magnetic characteristics in Fe-Si-B alloys containing less than 10 at % B has not been accomplished in the art.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a low boron amorphous alloy having excellent soft magnetic characteristics.

Our investigations led to the discovery that the addition of a small amount of P (0.02-2 at %)accomplishes the above-described described object. More specifically, we discovered that this small addition of P greatly improves the surface roughness of a cast alloy, thereby maintaining excellent soft magnetic characteristics even at a B content below that of conventional amorphous alloys.

That is, the present invention relates to a low boron amorphous alloy having excellent soft magnetic characteristics and having the following composition:

B: about 6-10 at %;

Si: about 10-17 at %;

P: about 0.02-2 at %; and

the balance Fe and incidental impurities. Accordingly it is important that the balance shall consist essentially of Fe and incidental impurities, and that the alloy of this invention shall consist essentially of the above atomic percentage of B, Si and P.

Further, the present invention relates to a low boron amorphous alloy having excellent soft magnetic characteristics and having the following composition:

B: about 6-10 at %;

Si: about 10-17 at %;

P: about 0.02-2 at %;

C: about 0.1-2 at %; and

the balance Fe and incidental impurities. Accordingly it is important that the balance shall consist essentially of Fe and incidental impurities, and that the alloy of this invention shall consist essentially of the above atomic percentage of B, Si, P and C.

When low boron amorphous alloys according to the invention are cast into sheets by a single roll method or other conventional technique, the surface roughness of the cast sheet is reduced to where the mean centerline surface roughness Ra on the casting mold side is 0.8 μm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between B and P contents and surface roughness in a Fe-Si-B amorphous alloy; and

FIG. 2 is a graph showing the relationship between P content and iron loss in Fe-Si-B amorphous alloys having three different B contents.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the results of an investigation into the effect of alloy composition on casting mold side surface roughness of cast alloys. This investigation was conducted on alloys comprising 78 at % Fe, and various quantities of Si, P and B. The alloys were made amorphous by conventional immediate-cooling techniques, such as the single roll method.

As seen in FIG. 1, the addition of P provides improved surface roughness at reduced B contents.

That is, an excellent mean centerline roughness of Ra ≦0.8 μm is obtained when P content is about 0.02-2 at % and B content is about 6-10 at %.

When alloys having compositions as described above are made amorphous using a conventional immediate-cooling device such as a single roll or the like, the surface roughness of resulting cast alloys can be limited to about 0.8 μm in terms of mean centerline roughness Ra on the casting mold side, whereby magnetic characteristics are improved.

It is preferable that the surface roughness Ra be about 0.6 μm or less to obtain even better magnetic characteristics.

FIG. 2 shows the results of an investigation into the relationship between P content and iron loss with respect to alloy sheets having the following compositions: Fe₇₈ Si_(9-a) B₁₃ P_(a) (comparative example having a large B content), Fe₇₈ Si_(14-a) B₈ P_(a) (example of the invention) and Fe₇₈ Si₁₆.5-a B₅.5 P_(a) (comparative example having a small B content). As shown in FIG. 2, when B content is about 8 at %, excellent iron loss characteristics are obtained over a P content range of about 0.02-2 at %.

Although the thickness of the alloy sheet is not particularly limited, if cast too thin, surface roughness deteriorates and magnetic flux density decreases. If cast too thick, the rate of cooling is insufficient and iron loss deteriorates. Thus, it is preferable that the sheet thickness be about 17-25 μm so that such problems are eliminated.

A description will be given below of suitable contents for the elements comprising the amorphous alloy of the invention.

B: about 6-10 at %

The upper limit of B content in the invention is about 10 at %. If the B content exceeds about 10 at %, the surface roughness of the alloy sheet increases whereby soft magnetic characteristics deteriorate. Further, production costs soar due to the large quantity of expensive ferroboron used.

The lower B content limit is about 6 at %, as making an amorphous alloy becomes difficult when the B content is below about 6 at %.

A B content of about 7.5-9.5 at % is preferred when the cooling capacity limits of industrial production machines and material costs are taken into account.

Si: about 10-17 at %

Si contributes to reduced magnetostriction and to improved thermal stability of the cast alloy. When Si content is less than about 10 at %, the reduction of magnetostriction is insufficient, whereas when Si content exceeds about 17 at %, sheet brittleness becomes a problem. Thus, Si content is limited to about 10-17 at %.

P: about 0.02-2 at %

In this invention, P is a particularly important element as it is indispensable to the realization of excellent surface roughness and soft magnetic characteristics. When P content is below about 0.02 at %, surface roughness fails to improve sufficiently, whereas when P content exceeds about 2 at %, sheet brittleness increases and thermal stability declines. Thus, P content is limited to a range of about 0.02-2 at %.

In a wide sheet which requires strict brittleness control and excellent thermal stability, it is preferable that P content be about 0.02-0.5 at %.

C: about 0.1-2 at %

C improves soft magnetic characteristics and stabilizes the yield of B when P is added. However, when C content is less than about 0.1 at %, these beneficial effects are not sufficiently realized, whereas when C content exceeds about 2 at %, thermal stability of the sheet is reduced. Thus, C is contained in a range of about 0.1-2 at %.

To maintain product stability in commercial production, it is preferable that C content be within a range of about 0.1-1 at %.

The invention will now be described through illustrative examples. The examples are not intended to limit the scope of the invention defined in the solicited claims.

Various molten alloys having the compositions shown in Table 1 were cast onto the surface a cooling roll (roll diameter: 280 mm) rotating at a peripheral speed of 27 m/sec, thereby producing amorphous alloy sheets.

The following characteristics were evaluated on each amorphous alloy sheet: roughness on the casting mold side, iron loss, magnetic flux density and sheet thickness. The results of the evaluations are shown in Table 1.

As revealed in Table 1, when B content was 10 at % or less (below conventional B content) and P was added in accordance with the present invention, excellent soft magnetic characteristics (comparing favorably to those of conventional alloys having large B contents) were obtained.

According to the present invention, a low boron amorphous alloy having soft magnetic characteristics of the same quality as high boron amorphous alloys can be obtained. Consequently, the invention requires less B, thereby sharply reducing production costs.

Although this invention has been described in connection with specific forms thereof, it will be appreciated that equivalents may be substituted for the specific elements described herein without departing from the spirit and scope of the invention as defined in the appended claims.

                                      TABLE 1                                      __________________________________________________________________________     (1)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     1    Fe.sub.78 Si.sub.9 B.sub.13                                                                1.0   0.100                                                                               1.530                                                                               25    Conventional Example                    2    Fe.sub.78 Si.sub.13.9 B.sub.8 P.sub.0.1                                                    0.25  0.101                                                                               1.521                                                                               23    Example of the Invention                h3   Fe.sub.78 Si.sub.12.9 B.sub.9 P.sub.0.1                                                    0.36  0.095                                                                               1.532                                                                               24    Example of the Invention                4    Fe.sub.78 Si.sub.13.4 B.sub.8.5 P.sub.0.1                                                  0.32  0.103                                                                               1.524                                                                               22    Example of the Invention                5    Fe.sub.78 Si.sub.14.4 B.sub.9.5 P.sub.0.1                                                  0.36  0.095                                                                               1.509                                                                               23    Example of the Invention                6    Fe.sub.78 Si.sub.11.9 B.sub.9 P.sub.0.1 C.sub.1                                            0.38  0.095                                                                               1.532                                                                               24    Example of the Invention                7    Fe.sub.78 Si.sub.9.9 B.sub.9 P.sub.0.1 C.sub.1                                             0.28  0.105                                                                               1.540                                                                               23    Example of the Invention                8    Fe.sub.78 Si.sub.16.4 B.sub.5.5 P.sub.0.1                                                  1.50  2.305                                                                               0.985                                                                               24    Comparative Example                     9    Fe.sub.78 Si.sub.10.9 B.sub.12 P.sub.0.1                                                   0.95  0.121                                                                               1.505                                                                               25    Comparative Example                     10   Fe.sub.78 Si.sub.8.9 B.sub.13 P.sub.0.1                                                    0.92  0.132                                                                               1.506                                                                               26    Comparative Example                     11   Fe.sub.78 Si.sub.13.5 B.sub.8.5                                                            1.05  0.195                                                                               1.479                                                                               23    Comparative Example                     12   Fe.sub.78 Si.sub.12.5 B.sub.9.5                                                            0.93  0.184                                                                               1.482                                                                               25    Comparative Example                     13   Fe.sub.78 Si.sub.13.98 B.sub.8 P.sub.0.02                                                  0.61  0.101                                                                               1.500                                                                               18    Example of the Invention                14   Fe.sub.78 Si.sub.13.8 B.sub.8 P.sub.0.2                                                    0.65  0.102                                                                               1.505                                                                               19    Example of the Invention                15   Fe.sub.78 Si.sub.12 B.sub.8 P.sub.2                                                        0.79  0.106                                                                               1.500                                                                               20    Example of the Invention                __________________________________________________________________________

                                      TABLE 1                                      __________________________________________________________________________     (2)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     16   Fe.sub.78 Si.sub.12.98 B.sub.8 P.sub.0.02 C.sub.1                                          0.41  0.102                                                                               1.504                                                                               20    Example of the Invention                17   Fe.sub.78 Si.sub.12.9 B.sub.8 P.sub.0.1 C.sub.1                                            0.53  0.101                                                                               1.505                                                                               19    Example of the Invention                18   Fe.sub.78 Si.sub.12.8 B.sub.8 P.sub.0.2 C.sub.1                                            0.54  0.103                                                                               1.506                                                                               17    Example of the Invention                19   Fe.sub.78 Si.sub.11 B.sub.8 P.sub.2 Cl.sub.1                                               0.69  0.105                                                                               1.510                                                                               19    Example of the Invention                20   Fe.sub.78 Si.sub.12.98 B.sub.9 P.sub.0.02                                                  0.55  0.102                                                                               1.512                                                                               19    Example of the Invention                21   Fe.sub.78 Si.sub.12.8 B.sub.9 P.sub.0.2                                                    0.58  0.098                                                                               1.514                                                                               18    Example of the Invention                22   Fe.sub.78 Si.sub.11 B.sub.9 P.sub.2                                                        0.52  0.096                                                                               1.515                                                                               18    Example of the Invention                23   Fe.sub.78 Si.sub.11.98 B.sub.9 P.sub.0.02 C.sub.1                                          0.42  0.097                                                                               1.520                                                                               20    Example of the Invention                24   Fe.sub.78 Si.sub.11.8 B.sub.9 P.sub.0.2 C.sub.1                                            0.51  0.101                                                                               1.518                                                                               20    Example of the Invention                25   Fe.sub.78 Si.sub.11 B.sub.9 P.sub.2 C.sub.1                                                0.58  0.095                                                                               1.515                                                                               20    Example of the Invention                26   Fe.sub.78 Si.sub.11.98 B.sub.10 P.sub.0.02                                                 0.50  0.094                                                                               1.520                                                                               19    Example of the Invention                27   Fe.sub.78 Si.sub.11.8 B.sub.10 P.sub.0.2                                                   0.51  0.097                                                                               1.521                                                                               18    Example of the Invention                28   Fe.sub.78 Si.sub.10 B.sub.10 P.sub.2                                                       0.53  0.098                                                                               1.523                                                                               23    Example of the Invention                29   Fe.sub.78 Si.sub.10.98 B.sub.10 P.sub.0.02 C.sub.1                                         0.43  0.095                                                                               1.524                                                                               19    Example of the Invention                30   Fe.sub.78 Si.sub.10.8 B.sub.10 P.sub.0.2 C.sub.1                                           0.42  0.094                                                                               1.520                                                                               19    Example of the Invention                __________________________________________________________________________

                                      TABLE 1                                      __________________________________________________________________________     (3)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     31   Fe.sub.78 Si.sub.9 B.sub.10 P.sub.2 C.sub.1                                                0.54  0.098                                                                               1.518                                                                               20    Example of the Invention                32   Fe.sub.76 Si.sub.14.98 B.sub.9 P.sub.0.02                                                  0.65  0.110                                                                               1.509                                                                               19    Example of the Invention                33   Fe.sub.76 Si.sub.14.8 B.sub.9 P.sub.0.2                                                    0.64  0.108                                                                               1.508                                                                               18    Example of the Invention                34   Fe.sub.76 Si.sub.13 B.sub.9 P.sub.2                                                        0.62  0.109                                                                               1.511                                                                               20    Example of the Invention                35   Fe.sub.76 Si.sub.13.98 B.sub.9 P.sub.0.02 C.sub.1                                          0.51  0.109                                                                               1.512                                                                               19    Example of the Invention                36   Fe.sub.76 Si.sub.13.8 B.sub.9 P.sub.0.2 C.sub.1                                            0.62  0.111                                                                               1.509                                                                               20    Example of the Invention                37   Fe.sub.76 Si.sub.12 B.sub.9 P.sub.2 C.sub.1                                                0.66  0.105                                                                               1.508                                                                               21    Example of the Invention                38   Fe.sub.76 Si.sub.14.48 B.sub.9.5 P.sub.0.02                                                0.43  0.080                                                                               1.503                                                                               18    Example of the Invention                39   Fe.sub.76 Si.sub.14.3 B.sub.9.5 P.sub.0.2                                                  0.44  0.078                                                                               1.501                                                                               18    Example of the Invention                40   Fe.sub.76 Si.sub.12.5 B.sub.9.5 P.sub.2                                                    0.57  0.083                                                                               1.505                                                                               18    Example of the Invention                41   Fe.sub.76 Si.sub.13.48 B.sub.9.5 P.sub.0.02 C.sub.1                                        0.49  0.095                                                                               1.503                                                                               19    Example of the Invention                42   Fe.sub.76 Si.sub.13.3 B.sub.9.5 P.sub.0.2 C.sub.1                                          0.58  0.093                                                                               1.504                                                                               21    Example of the Invention                43   Fe.sub.76 Si.sub.11.5 B.sub.9.5 P.sub.2 C.sub.1                                            0.53  0.097                                                                               1.505                                                                               19    Example of the Invention                44   Fe.sub.76 Si.sub.13.98 B.sub.10 P.sub.0.02                                                 0.57  0.105                                                                               1.504                                                                               19    Example of the Invention                45   Fe.sub.76 Si.sub.13.8 B.sub.10 P.sub.0.2                                                   0.53  0.102                                                                               1.505                                                                               21    Example of the Invention                __________________________________________________________________________

                                      TABLE 1                                      __________________________________________________________________________     (4)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     46   Fe.sub.76 Si.sub.12 B.sub.10 P.sub.2                                                       0.64  0.099                                                                               1.501                                                                               20    Example of the Invention                47   Fe.sub.76 Si.sub.12.98 B.sub.10 P.sub.0.02 C.sub.1                                         0.48  0.098                                                                               1.503                                                                               19    Example of the Invention                48   Fe.sub.76 Si.sub.12.8 B.sub.10 P.sub.0.2 C.sub.1                                           0.42  0.095                                                                               1.503                                                                               18    Example of the Invention                49   Fe.sub.76 Si.sub.11 B.sub.10 P.sub.2 Cl.sub.1                                              0.51  0.093                                                                               1.500                                                                               18    Example of the Invention                50   Fe.sub.80 Si.sub.11.98 B.sub.8 P.sub.0.02                                                  0.64  0.096                                                                               1.345                                                                               18    Example of the Invention                51   Fe.sub.80 Si.sub.11.8 B.sub.8 P.sub.0.2                                                    0.62  0.095                                                                               1.541                                                                               20    Example of the Invention                52   Fe.sub.80 Si.sub.10 B.sub.8 P.sub.2                                                        0.59  0.102                                                                               1.525                                                                               20    Example of the Invention                53   Fe.sub.80 Si.sub.11.88 B.sub.8 P.sub.0.02 C.sub.0.1                                        0.55  0.098                                                                               1.542                                                                               23    Example of the Invention                54   Fe.sub.80 Si.sub.11.7 B.sub.8 P.sub.0.2 C.sub.0.1                                          0.61  0.100                                                                               1.540                                                                               21    Example of the Invention                55   Fe.sub.80 Si.sub.9.9 B.sub.1 P.sub.2 C.sub.0.1                                             0.55  0.102                                                                               1.523                                                                               20    Example of the Invention                56   Fe.sub.80 Si.sub.9.98 B.sub.8 P.sub.0.02 C.sub.2                                           0.49  0.096                                                                               1.541                                                                               19    Example of the Invention                57   Fe.sub.80 Si.sub.9.8 B.sub.8 P.sub.0.2 C.sub.2                                             0.50  0.098                                                                               1.538                                                                               19    Example of the Invention                58   Fe.sub.80 Si.sub.8 B.sub.8 P.sub.2 C.sub.2                                                 0.51  0.104                                                                               1.526                                                                               18    Example of the Invention                59   Fe.sub.80 Si.sub.10.98 B.sub.9 P.sub.0.02                                                  0.63  0.092                                                                               1.542                                                                               21    Example of the Invention                60   Fe.sub.80 Si.sub.10.8 B.sub.9 P.sub.0.2                                                    0.61  0.094                                                                               1.543                                                                               19    Example of the Invention                __________________________________________________________________________

                                      TABLE 1                                      __________________________________________________________________________     (5)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     61   Fe.sub.80 Si.sub.9 B.sub.9 P.sub.2                                                         0.69  0.103                                                                               1.522                                                                               22    Example of the Invention                62   Fe.sub.80 Si.sub.10.88 B.sub.9 P.sub.0.02 C.sub.0.1                                        0.55  0.094                                                                               1.545                                                                               23    Example of the Invention                63   Fe.sub.80 Si.sub.10.7 B.sub.9 P.sub.0.2 C.sub.0.1                                          0.60  0.099                                                                               1.541                                                                               23    Example of the Invention                64   Fe.sub.80 Si.sub.8.9 B.sub.9 P.sub.2 C.sub.0.1                                             0.62  0.102                                                                               1.524                                                                               22    Example of the Invention                65   Fe.sub.80 Si.sub.8.98 B.sub.9 P.sub.0.02 C.sub.2                                           0.50  0.095                                                                               1.546                                                                               22    Example of the Invention                66   Fe.sub.80 Si.sub.8.8 B.sub.9 P.sub.0.2 C.sub.2                                             0.48  0.096                                                                               1.542                                                                               21    Example of the Invention                67   Fe.sub.80 Si.sub.7 B.sub.9 P.sub.2 C.sub.2                                                 0.65  0.101                                                                               1.521                                                                               18    Example of the Invention                68   Fe.sub.80 Si.sub.9.98 B.sub.10 P.sub.0.02                                                  0.64  0.088                                                                               1.541                                                                               19    Example of the Invention                69   Fe.sub.80 Si.sub.9.8 B.sub.10 P.sub.0.2                                                    0.69  0.087                                                                               1.540                                                                               23    Example of the Invention                70   Fe.sub.80 Si.sub.8 B.sub.10 P.sub.2                                                        0.72  0.099                                                                               1.523                                                                               19    Example of the Invention                71   Fe.sub.80 Si.sub.9.88 B.sub.10 P.sub.0.02 C.sub.0.1                                        0.68  0.089                                                                               1.545                                                                               18    Example of the Invention                72   Fe.sub.80 Si.sub.9.7 B.sub.10 P.sub.0.2 C.sub.0.1                                          0.61  0.087                                                                               1.546                                                                               22    Example of the Invention                73   Fe.sub.80 Si.sub.7.9 B.sub.10 P.sub.2 C.sub.0.1                                            0.57  0.100                                                                               1.522                                                                               20    Example of the Invention                74   Fe.sub.80 Si.sub.7.98 B.sub.10 P.sub.0.02 C.sub.2                                          0.49  0.094                                                                               1.545                                                                               21    Example of the Invention                75   Fe.sub.80 Si.sub.7.8 B.sub.10 P.sub.0.2 C.sub.2                                            0.48  0.095                                                                               1.547                                                                               21    Example of the Invention                __________________________________________________________________________

                                      TABLE 1                                      __________________________________________________________________________     (6)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     76   Fe.sub.80 Si.sub.6 B.sub.10 P.sub.2 C.sub.2                                                0.55  0.102                                                                               1.526                                                                               22    Example of the Invention                77   Fe.sub.78 Si.sub.13.88 B.sub.8 P.sub.0.02 C.sub.0.1                                        0.59  0.094                                                                               1.535                                                                               19    Example of the Invention                78   Fe.sub.78 Si.sub.13.7 B.sub.8 P.sub.0.2 C.sub.0.1                                          0.68  0.098                                                                               1.532                                                                               23    Example of the Invention                79   Fe.sub.78 Si.sub.11.9 B.sub.8 P.sub.2 C.sub.0.1                                            0.72  0.100                                                                               1.515                                                                               18    Example of the Invention                80   Fe.sub.78 Si.sub.1.98 B.sub.8 P.sub.0.02 C.sub.2                                           0.75  0.092                                                                               1.534                                                                               19    Example of the Invention                81   Fe.sub.78 Si.sub.11.8 B.sub.8 P.sub.0.2 C.sub.2                                            0.71  0.091                                                                               1.532                                                                               20    Example of the Invention                82   Fe.sub.78 Si.sub.10 B.sub.8 P.sub.2 C.sub.2                                                0.69  0.102                                                                               1.516                                                                               18    Example of the Invention                83   Fe.sub.78 Si.sub.12.88 B.sub.9 P.sub.0.02 C.sub.0.1                                        0.51  0.096                                                                               1.536                                                                               18    Example of the Invention                84   Fe.sub.78 Si.sub.12.7 B.sub.9 P.sub.0.2 C.sub.0.1                                          0.57  0 .094                                                                              1.532                                                                               22    Example of the Invention                85   Fe.sub.78 Si.sub.10.9 B.sub.9 P.sub.2 C.sub.0.1                                            0.59  0.101                                                                               1.518                                                                               23    Example of the Invention                86   Fe.sub.78 Si.sub.10.98 B.sub.9 P.sub.0.02 C.sub.2                                          0.57  0.095                                                                               1.538                                                                               18    Example of the Invention                87   Fe.sub.78 Si.sub.10.8 B.sub.9 P.sub.0.2 C.sub.2                                            0.58  0.093                                                                               1.532                                                                               19    Example of the Invention                88   Fe.sub.78 Si.sub.9 B.sub.9 P.sub.2 C.sub.2                                                 0.58  0.103                                                                               1.513                                                                               23    Example of the Invention                89   Fe.sub.78 Si.sub.11.88 B.sub.10 P.sub.0.02 C.sub.0.1                                       0.65  0 .093                                                                              1.536                                                                               21    Example of the Invention                90   Fe.sub.78 Si.sub.11.7 B.sub.10 P.sub.0.2 C.sub.0.1                                         0.67  0.094                                                                               1.531                                                                               20    Example of the Invention                __________________________________________________________________________

                                      TABLE 1                                      __________________________________________________________________________     (7)                                                                                                   Iron Magnetic                                                            Surface                                                                              Loss Flux Thickness                                     Specimen                                                                            Composition Roughness                                                                            W.sub.13/50                                                                         Density                                                                             of Sheet                                      No.  (at %)      Ra (μm)                                                                           (W/kg)                                                                              B.sub.8 (T)                                                                         (μm)                                                                              Reference                               __________________________________________________________________________     91   Fe.sub.78 Si.sub.9.9 B.sub.10 P.sub.2 C.sub.0.1                                            0.70  0.100                                                                               1.514                                                                               21    Example of the Invention                92   Fe.sub.78 Si.sub.9.98 B.sub.10 P.sub.0.02 C.sub.2                                          0.52  0.092                                                                               1.538                                                                               23    Example of the Invention                93   Fe.sub.78 Si.sub.9.8 B.sub.10 P.sub.0.2 C.sub.2                                            0.54  0.093                                                                               1.534                                                                               22    Example of the Invention                94   Fe.sub.78 Si.sub.8 B.sub.10 P.sub.2 C.sub.2                                                0.55  0.101                                                                               1.513                                                                               23    Example of the Invention                95   Fe.sub.76 Si.sub.14.38 B.sub.9.5 P.sub.0.02 C.sub.0.1                                      0.64  0.078                                                                               1.520                                                                               20    Example of the Invention                96   Fe.sub.76 Si.sub.14.2 B.sub.9.5 P.sub.0.2 C.sub.0.1                                        0.63  0.082                                                                               1.515                                                                               18    Example of the Invention                97   Fe.sub.76 Si.sub.12.4 B.sub.9.5 P.sub.2 C.sub.0.1                                          0.70  0.088                                                                               1.490                                                                               18    Example of the Invention                98   Fe.sub.76 Si.sub.12.48 B.sub.9.5 P.sub.0.02 C.sub.2                                        0.55  0.075                                                                               1.521                                                                               19    Example of the Invention                99   Fe.sub.76 Si.sub.12.3 B.sub.9.5 P.sub.0.2 C.sub.2                                          0.54  0.076                                                                               1.518                                                                               22    Example of the Invention                100  Fe.sub.76 Si.sub.10.5 B.sub.9.5 P.sub.2 C.sub.2                                            0.59  0.079                                                                               1.491                                                                               21    Example of the Invention                __________________________________________________________________________ 

What is claimed is:
 1. A low boron amorphous alloy having excellent soft magnetic characteristics, consisting of:about 6-10 at % B; about 10-17 at % Si; about 0.02-2 at % P; andthe balance Fe and incidental impurities.
 2. A low boron amorphous alloy having excellent soft magnetic characteristics, consisting of:about 6-10 at % B; about 10-17 at % Si; about 0.02-2 at % P; about 0.1-2 at % C; andthe balance Fe and incidental impurities.
 3. A low boron amorphous alloy cast sheet having excellent soft magnetic characteristics and having an alloy composition according to claim 1, wherein said cast sheet has a mean centerline surface roughness Ra on the casting mold side of about 0.8 μm or less.
 4. A low boron amorphous alloy cast sheet having excellent soft magnetic characteristics and having an alloy composition according to claim 2, wherein said cast sheet has a mean centerline surface roughness Ra on the casting mold side of about 0.8 μm or less. 